Hypochlorite ion is one of the reactive oxygen species of which actions in living bodies have been attracting attention in recent years. It is thought that the bactericidal action of neutrophils is mainly based on hypochlorite ions, and it has been demonstrated in vitro that hypochlorite ion is generated from hydrogen peroxide and chloride ion by myeloperoxidase in the azurophil granules (Klebanoff, S. J., and Clark, R. A. (1978), The Neutrophils: Function and Clinical Disorders, North-Holland Publishing Company, Amsterdam, Netherlands). Moreover, it is considered that hypochlorite ion plays an important role in injury of vascular endothelial surface in microcirculation dysfunction induced by the platelet activating factor (Suematsu, M., Kurose, I., Asako, H., Miura, S., and Tsuchiya, M. (1989) J. Biochem., 106, 355-360). However, since any perfect method of selectively measuring hypochlorite ions, especially in vivo measurement method, has not been established, it has been difficult to conclude that hypochlorite ion is directly involved in the aforementioned mechanism in living bodies.
It is thought that obstruction by reactive oxygen species over various physiologically active molecules and the like is involved in various diseases. Among these, reactive oxygen species having high oxidation ability such as hypochlorite ion, peroxynitrite, and hydroxyl radical give serious obstructions to living bodies, and therefore it is desired to provide a method for measuring these species in biosamples in living state with high sensitivity. Several fluorescent probes which can measure reactive oxygen species such as peroxynitrite and hydroxyl radical have hitherto been provided. For example, as a fluorescent probe for measuring reactive oxygen species, DCFH (2′,7′-dichlorodihydrofluorescein) and the like are known. However, DCFH cannot identify differences between reactive oxygen species, and is not capable of selectively measuring hypochlorite ion. Although it is known that hypochlorite ion can be measured by using the compounds disclosed in International Patent Publication WO01/64664 (Setsukinai, K., et al., J. Biol. Chem., 278, pp. 3170-3175, 2003), a combination of measurements may be needed to identify hypochlorite ion, and thus it has a problem that the operation is complicated.    Non-patent document 1: J. Biol. Chem., 278, pp. 3170-3175, 2003